BALTIMORE – Saying he was “swinging with one arm” during the Dodger series, Yankee right fielder Gary Sheffield was out of the starting lineup last night after an MRI in New York Monday revealed he has bursitis in his left shoulder.

Still, the diagnosis relieved Sheffield, who was told there was no structural damage.

Joe Torre doesn’t believe Sheffield will be placed on the disabled list. Sheffield also received a cortisone shot Monday.

“It just got to where I couldn’t even move it,” said Sheffield, who’d been bothered for the past few weeks by the bursitis.

“I thought there was something seriously wrong. Something major. I just tried to make it to the off day.”

The right fielder played through nagging hand and knee injuries earlier this year, and Torre hopes he’ll have his slugger back by the end of the series with the Orioles.

“He still manages to be a force, but you certainly don’t want him to be as uncomfortable as he’s been,” Torre said.

The Yankees (44-24) possess the deepest lineup in baseball, but any extended absence on Sheffield’s part will eventually be felt. The 35-year-old is batting .301 with 10 homers and 44 RBIs.

But he was 4-for-18 in his past five games, and his hits were all singles. Ruben Sierra played right field last night and was 0-for-4 in the Yankees’ 10-4 victory.

Sheffield was at Camden Yards early for ice and stimulation treatment on the shoulder. He believed he hurt the shoulder during the Oriole series at Yankee Stadium at the beginning of the month.

“I swung, fouled a ball back and it felt like my shoulder [dislocated],” Sheffield said. “I just took some time to gather myself.”

Before being checked out, he tried to get by on taking pain relievers, but eventually the shoulder even bothered him when he drove a car.

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Kevin Brown (strained lower back) definitely will not pitch this weekend, as Torre found out his starter probably won’t conduct a bullpen session until Friday. Initially, he believed Brown would possibly toss yesterday and tomorrow.

In the clubhouse before the game, Brown was seen doing exercises for the back – including one with a big red ball.

“When I said he was going to throw here, I was pretty much guessing,” Torre said. “But the therapy he’s getting, that’s the game plan. There’s therapy that he should start throwing on Friday.”

Rookie Brad Halsey will pitch against the Mets Friday, and Jose Contreras will go Saturday. Halsey could “possibly” be making a few starts, Torre said.

A possible rehab assignment could be on tap for Brown, who is eligible to come off the DL this weekend.